Although a curable epoxy resin composition that contains a halogenated epoxy resin or an antimony-type oxide such as an antimony trioxide produces a curable body with good resistance to combustion, when it burns it either generates toxic gases or a toxic antimony trioxide substance, which result in undesired impact on human health and environment. On the other hand, curable epoxy resin compositions that contain aluminum hydroxides, magnesium hydroxides, or similar metal oxides and phosphorus-type flame-retardants, or the like, have low moldability and low resistance to moisture in a cured body.
On the other hand, known in the art are the following compositions: a curable epoxy resin composition prepared from an epoxy resin, a curing agent, and a silicone resin with an epoxy-containing organic group and a phenyl group (see Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) 6-298897 and corresponding U.S. Pat. No. 5,952,439); a curable epoxy resin composition prepared from an epoxy resin, a curing agent, and a silicone resin with an epoxy-containing organic group (see Kokai 9-208806 and corresponding U.S. Pat. No. 5,891,969); and a curable epoxy resin composition prepared from an epoxy resin, curing agent, inorganic filler, and a silicone resin with a phenyl group and an alkoxy group (see Kokai 11-323086).
However, when the inventors of the present invention studied the curable epoxy resin composition disclosed in Kokai 6-298897, they found out that resistance of this composition to combustion can be drastically improved if the epoxy resin is represented by a crystalline epoxy resin and the curing agent is represented by a phenol resin. Furthermore, while studying the curable epoxy resin disclosed in Kokai 9-208806, the inventors of the present invention revealed that, if the amount of phenyl groups is less than 10 mole % relative to the total content of organic groups in the silicone resin, the aforementioned silicone resin cannot be efficiently dispersed in the epoxy resin, and the obtained cured body does not acquire sufficient resistance to combustion. The results of the inventors' study aimed at properties of the curable epoxy resin composition disclosed in Kokai 11-323086 showed that the silicone resin contained in this composition is subject to bleeding and therefore contaminates the mold. In addition, it has poor moldability, and the obtained cured body does not possess sufficient resistance to combustion.
As a result of the aforementioned studies, the inventors arrived at the present invention.
It is an object of the present invention to provide a curable epoxy resin composition which is characterized by good moldability, demonstrates excellent resistance to combustion in a cured body, is free of a halogenated epoxy resin and antimony oxides, and therefore does not produce an unfavorable impact on human health and environment.